Greediness isn't just about money: people can be greedy about time, too. And it is just as negative. So if you feel like someone is demanding too much of yours, it's perfectly fine to say something to them about it. Make it clear that while you enjoy spending time with them, you have your own life to lead. Too many people tie their identity to the identity of someone else, and you shouldn't encourage that. You're your own person, and they should be, too.